The invention concerns a tubular burner provided with a Venturi tube arranged at the inside of the body of the burner, a mixture of air and fuel being fed to the burner through the Venturi tube. The mixture is discharged from the body of the burner through openings made on a diffuser portion of the body and is then caused to burn.
Tubular burners are known having a tubular body, with circular or elliptic cross section, and a Venturi tube coaxial with the burner body. A limited volume is defined at the inside of the burner body between the inner surface of the burner body and the outer surface of the Venturi tube. The flow of the air and fuel mixture, which is discharged from the Venturi tube, must reverse its own direction of flow in order to enter said limited volume and reach said openings. Said reversal of flow direction causes high losses of energy and considerable variations of the values of the characterising parameters of the mixture discharged from said openings, such as pressure, speed, air/fuel rate, over said diffuser portion Said variations leads to incorrect combustion of the mixture of air and fuel, which is not acceptable and can be remedied with great difficulty. Said incorrect combustion may cause, for instance, flame detachment or an increase of the harmful emission of the burner.
Someone has tried to eliminate said drawbacks by arranging the Venturi tube in such a position that the axis of the Venturi tube is separate from the axis of the burner body, particularly by shifting the Venturi tube downward with respect to the diffuser portion of the burner body However, said solution has proved to be unsatisfactory because of an increase of losses of energy at the inside of the burner body caused by the asymmetric position of the Venturi tube.
A further drawback in the known tubular burners, caused by variations of the values of the characterising parameters of the air-fuel mixture discharged from said openings, is a local overheating of the surface of the burner body. Said local overheating is caused by the fumes produced by the combustion that lick the surface of the burner body near said diffuser portion and transmit heat to the burner body by convection.
The present invention intends to overcome the drawbacks mentioned above.
According to the present invention, there is provided a tubular burner having a body on the surface of which openings are made for discharging a mixture of air and fuel fed to said body through a Venturi tube arranged at the inside of said body, characterized in that said body has a cross section shaped in such a way that the distance between the outer wall of the Venturi tube and the inner wall of said body, when measured in a radial direction of said Venturi tube, has a first value substantially constant in a first portion of the perimeter of the Venturi tube and a second value greater than said first value in a second portion of said perimeter.
That makes possible to make available for the flow of said mixture discharged from the Venturi tube a volume wide enough to allow said flow to reverse the direction of its motion between the outlet of the Venturi tube and the openings made in the burner body without causing variations of the values of the characterising parameters of said mixture across said diffuser portion, when the mixture is discharged from said openings.